Uncovering Jupiter’s mysteries

How was Jupiter formed? Does it have a solid core? How much water is present within its deep atmosphere? These are some of the questions scientists are looking forward to answering with the data collected by Juno, the space probe that entered the orbit of our solar system’s largest planet on July 4 after a five-year journey. A collaboration between NASA and European scientists, the mission is powered only by solar panels. John Leif Jørgensen, a co-investigator who heads Measurement and Instrumentation at the Technical University of Denmark’s DTU Space, discusses the three-year mission.

TECHNOLOGIST How did you get involved in this project?

JOHN LEIF JØRGENSEN It all started long before the idea of Juno was even born. In the 1990s I was working in an astronomical observatory in Hawaii. At that time I had developed a totally new instrument for the first Danish national satellite. Called a star tracker, it was a camera used for precise navigation and photography. One night I was dining with some colleagues, and this guy from NASA came over and asked me whether I was the Dane who had developed the star track system and if I thought it could work further out in space, in Jupiter’s environment. I didn’t believe this technology could be stretched that far, but he asked me to look into it and we began to work together. That was the start of my involvement in what later became Juno.

TECHNOLOGIST What is the mission’s main goal?

JOHN LEIF JØRGENSEN We are trying to better understand how Jupiter was formed, as the current model explains the formation of all planets in our solar system pretty well except for Jupiter.

The other big question is to better define the morphology of the planet, which is a gargantuan gas cloud. If it had twice its current mass, Jupiter would probably ignite like a small sun. We know that Jupiter emits twice as much energy as it collects from the Sun, but we don’t know where that energy comes from. We also suspect the presence in the middle of Jupiter of a rock body the size of Earth or larger, so that’s another thing we’re looking for.

Finally we’re trying to solve the mystery of missing water on Jupiter. Shooting stars, which are mainly composed of water, deliver about 8 tonnes of water to Earth every day. As they enter our atmosphere they are ionized, creating the stream of light that we know. Jupiter, being a far bigger gravity trap, should be soaking wet. But we can’t find any water there. So all in all the planet is very enigmatic, and many of our theories about gas giants seem to be wrong.

TECHNOLOGISTWhat part of the mission did DTU Space work on?

JOHN LEIF JØRGENSEN Our contribution was to develop a new star tracker that could work in an extreme environment such as Jupiter’s. The temperature out there is -200° C, and the planet is surrounded by a violent radiation field, the worst in our solar system. The planet’s distance from the sun also means that solar panels are really inefficient. From 2005 to the launch in 2011, we designed methods to work around these problems. It’s been a sizeable effort by DTU, but then again we’re responsible for about a fifth of the science from the spacecraft. When building the instrument, around 20 people from DTU were involved in the project. Currently, about 12 of us work on analysing the data sent in by Juno.

TECHNOLOGIST What were the biggest challenges on this project?

JOHN LEIF JØRGENSEN There were two types: organisational and technological. When NASA spends €1.1 billion on a mission, everything has to work. So there were lots of technical reports, analyses and meetings in which we had to defend our solutions before the world’s top experts. And on the technological side, we had to get the equipment to function, which was not trivial. All in all, we were fighting on two fronts at the same time, which is kind of unusual in the research world. Normally, you first work on cracking the technological code before going on to convince the industry or an end-user of your product’s worth. It surprised me how hard that actually was, how much time and energy it required.

TECHNOLOGIST What have your cameras been doing since the launch?

JOHN LEIF JØRGENSEN We’ve been tracking the spacecraft’s altitude and we’re looking forward to capturing images of different regions of the planet, notably the lightning strikes that take place on the dark side of Jupiter, as well as its ring system, about which we know very little.

In 2013 we captured images of Earth during a so-called swing-by manoeuvre. The sequence, filmed from 4 million kilometres away, shows the Earth approaching like a spaceship. It was the first time this had been done, and it’s now one of NASA’s most viewed videos. Our purpose was to validate a new optical navigation method.

During our journey, we also used the cameras to look for so-called zodiacal dust, which some believe to be remnants of the formation of our solar system. We also trained our cameras to look for smaller asteroids in the solar system, since the size limit of objects visible through our biggest telescopes is about 800 metres across.

TECHNOLOGIST What is your current day-to-day work like?

JOHN LEIF JØRGENSEN The spacecraft is now 48 light minutes away from Earth, which means that every command takes 48 minutes to reach the spacecraft, and the same amount of time is needed to get a signal back. The timing is simply not practical, especially because we must go through the Deep Space Network antennas – gigantic installations distributed around the world, the use of which we share with other missions. A lot of the work is really planning and pre-programming.

TECHNOLOGIST How long will you be involved on this mission?

JOHN LEIF JØRGENSEN Till the bitter end! (Laughs.) We currently fly on a highly elliptical orbit to avoid Jupiter’s radiation field, but the spacecraft will gradually be pulled down and exposed to higher radiation. Finally, in about three years, we will crash the satellite into the clouds of Jupiter where it will burn up, to avoid contaminating other solar system bodies – such as Jupiter’s moons.

TECHNOLOGIST How has the international collaboration worked out?

JOHN LEIF JØRGENSEN We have a fabulous collaboration with our colleagues. But because we generate 100 times more data than we can get back to Earth, there is a constant struggle to get a little more data, just like siblings quarrelling when there is too little meat on the dinner plate.

TECHNOLOGISTWhat lessons have you learned from working on the mission?

JOHN LEIF JØRGENSEN When I started to work in this business, I thought space missions were expensive because of companies’ and people’s greed. But I’ve learned that space really is that challenging. All the money goes into solving incredibly difficult problems, from both technological and organisational standpoints. The thing is, it takes half a career to fly a spacecraft like this: I started in the Juno mission in 1995, we reached Jupiter this year and will only receive all the data produced in three more years. We’re doing this for the history books. It has been extremely hard work, but it’s also been a lot of fun.